Methods for the characterisation of hybrid energy storage system for independently powered trains

Servatian, Dena (2021). Methods for the characterisation of hybrid energy storage system for independently powered trains. University of Birmingham. Ph.D.

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Abstract

The UK has set a new target for reducing carbon emissions by 57% by 2030 and 80% by 2050 compared to the carbon emission level in 1990. In the UK, transport contributes to a quarter of the overall carbon emissions. Although the railway is considered one of the most environmentally-friendly modes of mechanised transport, it should be ensured that the railway sector plays its role in this new target and that its share of carbon emissions is reduced. Currently, about 29% of the UK’s fleet is diesel-only, and phasing out these types of trains by 2040 is part of the Carbon Emission Reduction plan. In order to reach this goal, either railway lines should be electrified or on-board energy storage systems should be installed above the trains. While electrification appears to be an efficient and clean method, it is time-consuming and initial costs are high. Installing on-board Energy Storage Systems (ESSs) including batteries, supercapacitors or fuel cells is a zero-emission and cost-effective approach to phasing out the remaining diesel trains in the UK and, consequently, contributing to the Carbon Emission Reduction plan. This thesis aims to propose an on-board ESS for independently powered trains where the ESS supplies all the energy required for the train traction.
This thesis begins with a review on the previous researches on Hybrid Energy Storage Systems (HESSs) including batteries and supercapacitors in power applications and specifically in the railway sector. It reviews the reasons for employing an HESS and the sizing methods.
Following this, the gap in sizing and charging an HESS for an independently-powered train is discussed and the hypothesis is developed.
The first phase of this thesis analyses the use of batteries and supercapacitors together in an HESS in order to evaluate the efficiency of integrating these two energy storage devices in terms of the weight and volume of the HESS. Various scenarios with different configuration of batteries and supercapacitors are considered to provide the required energy and power demand in the traction. Hence, the total size of the HESSs and performance of the sized HESSs in all scenarios are compared. Furthermore, it considers the influence of the energy density and power density of the battery and supercapacitor on the total size of the HESS. This phase also evaluates the effect of the C-rate of the battery on the total size of the HESS as well on the performance of the battery.
In the second phase of this thesis, an HESS including batteries and supercapacitors is sized optimally by employing the Frequency Analysis method. The objective function of the optimisation is to minimise the weight and volume of the HESS based on the power profile, where decreasing the weight of the on-board HESS decreases the mass of the train and consequently, the energy consumption. Low-pass and high-pass filters with optimal cut-off frequencies (achieved by Brute Force optimisation) are employed to split the journey into the low frequency and high frequency parts of the load so that batteries are in charge of supplying the low-frequency parts and supercapacitors can provide power to the high-frequency parts. Furthermore, this phase proposes the use of batteries to act as the energy supply and charge supercapacitors during the journey in order to meet the energy and power demand.
The two phases are applied to two case studies in order to validate the results. The first case study is a diesel line from Bidston Station to Shotton Station in Liverpool where the on-board HESS can be installed above the Electrical Multiple Unit (EMU) running on this line to provide the energy required for the return journey. The second one is a tram line in Edinburgh where the installed on-board HESS could be a substitute for overhead electrification. These journeys are simulated in Single Train Simulator (STS) in MATLAB in order to achieve some precious data such as energy consumption and peak power requirement.
The key findings of this thesis are that the integration of batteries and supercapacitors in an HESS is an efficient choice for independently powered trains the HESS can be optimally sized using Frequency Analysis method and supercapacitors can be charged by batteries during the journey.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):